In the past, many apparatuses and processes have been developed for discharging a fibrous, cellulosic, material suspension from a container such as a bleaching tower. These prior apparatuses and processes have numerous disadvantages to them.
One example of a prior discharge assembly is disclosed in Austrian Patent No. 387,995. This Austrian Patent discloses a discharge system in a container with a central bottom discharge and a rotating conveying arm, wherein a central discharge pipe simultaneously serves as a drive for the conveying arm and for conveying the stock. No dilution of the medium to be discharged is provided by this high, consistency, discharge system in the stacking or bleaching tower. In other words, the consistency or the solid content of the discharged medium is the same as the consistency or the solid content of the medium on charging.
In other discharge systems, treatment of the medium to be discharged is accomplished by the two-step bleaching system. In a two-step bleaching system, chemical pulp is typically stored with a medium consistency range of a solids content between from about 12 to 25 percent before being fed to dewatering machines and subsequent to the required dilution of the medium. The discharge consistency of the medium from the stacking or bleaching tower should be adjustable to between 3 and 15 percent to adjust the consistency to the particular dewatering machines disposed downstream. Material of such a discharge consistency could be pumped off by rotary or centrifugal pumps. The required dilution of the discharge of the pulp suspension from the stacking or bleaching tower is usually effected in a separate diluting vat. Circulation of the pulp suspension in this diluting vat is effected by a circulation agitator. This system has the drawback that it requires a separate diluting vat.
In another prior discharge system, the discharge of the pulp suspension from the stacking or bleaching tower is diluted in a diluting zone adjacent the bottom space of the stacking or bleaching tower. In this case, circulation of the pulp suspension in the diluting zone is effected by a circulation agitator. However, in order to support the pulp circulation, a portion of the pulp suspension pumped off after dilution must be recycled to the diluting zone. This discharge system has the drawback that the pulp consistency still ranges from about 5 to 6 percent even after dilution. The uncontrollable zone height results in different dwell times for the pulp suspension in the bleaching tower. Finally, a large diluting space in relation to the bleaching or stacking volume is required.
Another discharge system is disclosed in European Patent Application 269,124, which discloses adding a diluting liquid to the fibrous material suspension or medium through agitating arms disposed in the area of the container bottom to reduce the solids content of the suspension or medium to be discharged. However, this discharge system has the drawback that the orifices in the agitating arms for adding the diluting liquid often become clogged by the medium to be discharged.